The present invention is directed to a reader apparatus of the type which projects a magnified image of a film frame onto the rear side of a viewing screen to facilitate forward viewing of the magnified image. The invention is more particularly directed to an improved microform reader which includes an adjustable mirror assembly for optimizing the brightness of the displayed image on the viewing screen and an adjustable lens assembly which allows the optical axis of the projection lens assembly to be adjusted for perpendicularity to the image frame surface.
Microform readers are well known in the art and provide greatly magnified images of single film frames of a roll of microfilm, microfiche, or ultrafiche for viewing purposes. Although the present invention is equally applicable to any microform reader, the preferred embodiment herein will be directed to an ultrafiche readers. Such devices generally include a light source, a condensing lens, and a projection system for magnifying and projecting a magnified image of a film frame image onto a viewing screen. Inasmuch as the film frame images are extremely small relative to the displayed image, and therefore greatly magnified, the position of the various elements of such a reader is critical.
In particular, the light directed through the condensing lens must be of an intensity which allows the displayed image to be of adequate brightness for viewing purposes. Such readers generally include a mirror positioned between the light source and condensing lens for directing the light emitted from the light source through the condensing lens and thus through the film frame image to be displayed. The relative position of the mirror is critical to provide adequate viewing brightness. Additionally, the projection lens assembly which magnifies the image frame must be postioned such that its optical axis is perpendicular to the film frame surface to assure proper focusing for the entire film frame. Inasmuch as the film frame is being magnified a great number of times, slight variations in the normality of the axis of the projection lens assembly to the surface of the image frame can cause portions of the displayed images to be out of focus. Therefore, it is essential that the optical axis of the projection lens be perpendicular to the film frame surface.
The critical positioning of the above mentioned elements of such readers is generally obtainable with readers constructed of metallic materials but the problems associated with their relative positions are greatly magnified when the readers have housing component parts constructed out of plastic. This obtained because the non-uniformities in the plastic forming process and extraction of the elements from their molds cause the plastic parts to be generally non-uniform. To overcome there difficulties, it is therefore disirable to provide an adjustable mirror assembly for optimizing the brightness of the displayed image and an adjustable projection lens assembly which allows the optical axis of the projection lens assembly to be adjusted for perpendicularity to the film frame surface.
It is therefore a general object of the present invention to provide an improved microform readers apparatus.
It is another object of the present invention to provide an improved microform reader apparatus which includes an adjustable mirror assembly to optimize the brightness of the displayed images.
It is still a more particular object of the present invention to provide a microform reader having an adjustable mirror assembly which is adjustable from the front of the ultrafiche reader to allow simultaneous monitoring of the brightness of the displayed image as the position of the mirror is adjusted.
It is a further particular object of the present invention to provide a microform reader which has an adjustable projection lens assembly which allows the optical axis of the projection lens assembly to be adjusted for perpendicularly to the image frame surface.